Fractionation process



Jan. 12, 1960 R. N. FLEcK ETAL 2,921,025

FRACTIONATION PROCESS Filed July 13, 1956 l 3 Sheets-Sheet 2 Jan. 12,1960 R. N. FLECK ET AL 2,921,026

FRACTIONATION PRocEss 3 Sheets-Sheet 3 Filed July l5, 1956til/514414151419# 'United vStates Patenti() FRAcnoNA'rroN rRocEssApplication July 13, 1956, Serial No. 597,742 7 claims.y (ci. 20s- 310)This invention relates to the fractionation of Huid mixtures, eithergaseous or liquid, such as mixtures of hydrocarbons. 'Ihe inventionrelates particularly to an improved process for the fractionation ofcomplex hydrocarbon mixtures in lthe gasoline boiling range to produce ahigh antiknock rating gasoline through the selective removal of lowantiknock rating components.

Gasoline improvement to raise the antiknock rating is required toprovide an adequate fuel for modern high compression internal combustionreciprocatingpiston engines. Gasoline in general comprises manyindividual components, including hydrocarbons having between about 4 andabout 12 carbon atoms per molecule. In this range are found manystraight and branched chain parain hydrocarbons, straight and branchedchain olefin hydrocarbons in cracked gasolines, as well as manynaphthene and aromatic hydrocarbons. The complexity of gasoline stocksis appreciated by the fact that there are some 660 possible parainisomers and over 3800 olefin hydrocarbon isomers in this range of from 4to 12 carbon atoms per molecule. In addition there are a great manynaphthene and aromatic hydrocarbons. Each component has its own tendencyto knock in internal combustion engines and its molecular characterstrongly governs this tendency. In general the straight chain or normalpara'lin hydrocarbons have the greatest tendency to knock and thereforehave the lowest antiknock rating. The naphthene hydrocarbons havingslightly higher antiknock rating, followed by the normal oleins, theiso-olefins, the iso-parains, and the aromatic hydrocarbons have thehighest antiknock rating. p

The gasoline is a mixture therefore that has an antiknock rating whichis a function of its composition. Straight-run gasoline generally has alow rating due to its relatively high normal parain content andrelatively low iso-paraflin and aromatic content. Cracked gasolines onthe other hand have higher antiknock ratings due to the presence ofnormal and iso-olefin hydrocarbons. Distillation alone is not especiallyeffective in removing only the low antiknock rating components since therating is essentially determined by molecular structure rather thanboiling point.

'In the past, elective antiknock rating increase has been accomplishedby the addition of materials to the gasoline such as antiknock agentslike tetraethyl lead and hydrocarbon components of very high knockratings such as high branched chain hydrocarbons like the alkylate ofiso-butane and iso-butylene, or aromatic hydrocarbons, and the like.Antiknock rating increase is also obtainable by high temperaturetreatment such as thermal or catalytic cracking, dehydroaromatization orreforming, and the like. Such treatment effectively converts some of thelow antiknock rating components into components having higher knockratings.4

The addition of antiknock agents or of hydrocarbons of unusually 'highantiknock rating is expensive sincev usually they must be purchased orsynthesized for`such use. Even the high temperature treatments to raisethe knock rating is only partly elective since the product from theseprocesses still contains appreciable quantities of low antiknock ratingmaterials. For example, a desulfurized naphtha having a knock rating of51 (F-l clear) is reformed to effect dehydrogenation of normal parainsand cyclization to form aromatics over a platinum catalyst to produce aproduct having a knock rating of 96 (F-l clear). Although this knockrating is satisfactory in some cases, the product still contains about13% by volume of normal parains whose antiknock rat ings were of theorder of 20 or less. y v

The present invention is therefore directed to an improved process forincreasing the antiknock rating of straight-run or cracked gasolineswithout high temperature treatment, and which is also applicable to theimprovement of fairly high antiknock rating gasolines such as thoseproducedin high temperature thermal or catalytic treatments.Specifically the process comprises the separation of low antiknockcomponents from these materials so as to leave only the high antiknockrating materials. The process involves the selective adsorption ofnormal parathns or normal olelns from the mixture of hydrocarbons on thebasis of their straight chain molecular shape. The process however doesnot require the usual high temperature desorption of the rich adsorbentwhich is conventionally used in all other adsorptive fractionationprocesses. Thus the adsorbent saturated with low antiknock ratingcomponents need not be heated, or stripped with a stripping gas, orboth, to render it reusable in the process. Rather, theadsorbent issubjected to a novel and simple treatment in'which an active exchange ordisplacement of the low antiknock rate materials is effected by means ofa selected recycle stream of adsorbable hydrocarbons.` The processthusproduces an unadsorbed or raiiinate stream of gasoline containing therecycle component which can be separated from the nonadsorbed materialby ordinary distillation, and a desorbed or extract'gasoline streamincluding adsorbed low antiknock rating materials together with therecycle component, which is also readily separable therefrom bydistillation.

dt is therefore a'primary object of this invention to provide animproved fractionation process using a specific adsorbent which isactive in adsorbing materials on the basis of their molecular size orshape.

It is a further object of `this invention to provide an improvedselective adsorption and distillation process for the fractionation ofcomplex mixtures and which is characterized by the absence of the usualhigh temperature adsorbent-desorption treatment. p

It is a specific object of this invention to provide a fractionationprocess for the separation of complex mixtures using aV specificadsorbent, which selectively adsorbs components having linearor straightchain molecules, and including a desorption step which involves anexchange displacement with a recycle stream containing a substantialproportion of components having linear or straight chain molecules andwhich are readily separable, by virtue ofa substantially differentboiling point or range, from the straight chain materials adsorbed fromthe complex mixture.

It is a more specific object of this invention to provide an improvedcontinuous process for gasoline fractionation to remove low antiknockrating components there' from by alternately contacting a substantiallycompact bedof solid granular adsorbent with the gasoline fraction toadsorb straight chain oleiins and parains therefrom,`

then contacting the adsorbent with a recycle stream of hydrocarbonsreadily separable by distillation from the feed stream and consisting ofother straight chain olens or paraftins-so as to displace .thecomponents adsorbed: from the gasoline fraction and pre-saturate theadsorbent with straight chain components from the recycle stream,

and nallydistilling both the unadsorbed raffinate fraction and thedesorbed or displaced extract fraction from vthe `adsorbent so as tolseparate the straight chain recycle materials therefrom leaving anunadsorbed gasoline fraction of high antiknocky rating and an adsorbedgasoline fraction of very low antiknock rating.

Other objects of the present invention will become apparent to thoseskilled in the art as the description and illustration thereof proceed.

Briefly the present invention comprises an improved fractionationprocess involving a combination of selective adsorption on a granularsolid adsorbent anddistillation of the fluids being treated so as toeffect an improved separation of complex mixtures of components on thebasis of their molecular species. The present invention will bedescribed in connection with fractionation of a mixture or" a complexmixture of hydrocarbons of the gasoline boiling range. Such `mixturescontain many different hydrocarbon components having from about 4 toabout 12 carbon atoms per molecule and which components are of diiferentmolecular species.. The feed mixture, herein considered to be gasolinefor purposes of example, is first passed through contact with a compactbed of solid granular adsorbent to adsorb more readily adsorbableconstituents leaving the less readily adsorbable constituents as anunadsorbed raffinate phase. Instead of heating the resultant richadsorbent and contacting it with a stripping fluid as in conventionaladsorptive fractionation processes, in the present invention this richadsorbent containing the more readily adsorbable constituents of thefeed is contacted with a recycle stream ofA hydrocarbons containingadsorbable components and selected to have a boiling point or boilingrange sufficiently different from that of both the adsorbed andunadsorbed phases of the feed gasoline that it may readily be distilledfrom the unadsorbed as well as from the adsorbed fractions of the feed.An active exchange displacement occurs in which the adsorbable recyclestream is adsorbed in exchange with and displacing the feed componentspreviously adsorbed. This removal of the more readily adsorbableconstituents in the adsorbed phase from the adsorbent by'contacting therich adsorbent with a recycled exchange Vdisplacement stream produces anextract stream comprising a mixture of the desorbed more readilyadsorbable constituents of the feedstock plus the constituents of therecycle stream andk the adsorbent is left saturated with recycle streamcomponents. The extract stream is then distilled to recover the desorbedfraction from the recycle components. The adsorbent is then contactedwith further quantities of the feedstock in which the more readilyadsorbable components exchange with and displace the recycle componentspresent on theadsorbent and produce a raflinate stream containing theunadsorbed components of the feed gasoline plus the desorbed recyclecomponents. This eluent rainate stream is also distilled Vto separatethe unadsorbed fraction from the recycle components.

The recycle stream employed in the process of this invention forexchange displacement of the adsorbed feedstock materials from theadsorbent may be a mixture of adsorbable components, or a single pureadsorbable component,V naturally occurring in the feedstock. TheVrecirculavted material however must have a different boiling point orboiling range from the boiling point or boiling range of the feedstockso that it is readily and economically separable from both the adsorbedphase components and the unadsorbed phase components of the feedstock.In the process the raffinate stream of unadsorbedy materials from theadsorption zone as well as the extract stream of displaced'adsorbedmaterials, both con tain the recycledidisplacementexchange materials.Each of these streams is separately distilled, the recycle cornponentsare recirculated in the process to effect exchange displacement fromthe. rich adsorbent, and theunad:

sorbed gasoline hydrocarbons and the adsorbed gasoline hydrocarbons areproduced as separate products of the process. The character andantiknock rating of the hydrocarbons in these two product streams aregoverned by the nature of the selective adsorbent used in the process.With the adsorbent more particularly described below, only normal orstraight chain paraflins, and normal olens if present, are adsorbable.Therefore the extract phase displaced from the adsorbent contains therelatively low anti-knock rating materials. The unadsorbed rafnate phasecontains the branched chain and naphthene and aromatic hydrocarbonswhose molecular size renders them unadsorbable.

The adsorbent employed in the process of this invention is a solidgranular material having a mesh size range between about 2 and 100 meshand preferably between about 4 and about 30 mesh. It is used in the formof a dense compact bed of material through which the feed anddisplacement and exchange recycle streams pass, either in the vaporphase or in the liquid phase. The process may employ the adsorbent inthe form of a single static bed of material in which case the process isonly semicontinuous. Preferably a plurality of two or more static bedsof adsorbent are employed with appropriate remotely operable valving sothat the feed stream is passed through one or more of the adsorbers in aset while the exchange displacement stream passes through one or more ofthe other adsorbers in the set. In this case the feed and product flowsare continuous, in either the vapor or liquid phase, and either upordown through the adsorbent. When the granular adsorbent is suincientlyrugged physically then the moving solids bed modification may beemployed in which flow of feed is maintained continuously through anadsorption zone, the low of displacement exchange fluid is maintainedcontinuously through a desorption zone, and the granular adsorbent isrecirculated successively through these two zones. With the smallersized mesh ranges of adsorbent, the material may be iluidized in and bythe iluid streams contacting it, although the compact bed modificationsare preferred since a greater number of theoretical and actual contactstages are more readily obtained in smaller and simpler equipment.y

The adsorbents employed in practicing the present invention are thenatural or synthetic zeolitic crystalline partially dehydrated metalloalumino silicates. The composition of one typical synthetic zeolitehaving a pore size of about 4 A. is [Na2O'Al2O3- (Si02) 2]. It may beprepared by heating stoichiometric quantities of alumina and silicaand,v excess caustic under pressure. The excess is washedk out and thedesired metal ion may then be introduced by ion exchange. Part of thesodium in this material can be ion exchanged with` concentrated saltsolutions at superatmospheric pressure and temperatures of 300 C. tointroduce other-metal-ions-such as calcium to produce having a poresizeof about 5 A. Certain naturally occurring minerals, such aschabazite, analcite, gmelinite, and the like, can be heated to dehydratethe molecule and obtain an activatedY zeolitic adsorbent similar inadsorption properties to the manufactured materials. These naturalandsynthetic materials are all zeolites and their sodium and calciumderivatives areA very stable adsorbents which apparently have poresavailable for adsorption which are quite uniform in size.k Otherderivatives have different sized pores The molecules which are the morereadilyadsorbable and for which the adsorbent exertsV preferentialadsorptive forces are those having straight chainemolecules whoseminimum dimensions are equal to or slightly less than these poredimensions. Thus the normal parains and normal olenswith cross chaindimensions of under 5 A..are.ver,y strongly and very readily adsorbedbythesematerials. However the branched chain parafiins or olefins, and thenaphthene and aromatic hydrocarbons, all having molecular dimensions inthe shortest direction in excess of 5 A. are substantiallynonadsorbable. These adsorbents are thus selective for normal paraliins,and normal olefins if presentyand will not adsorb any appreciablequantity of other hydrocarbons. Other derivatives of these particularinorganic adsorbent materials'have uniformly sized pores as high as from12 to 13 A. and these will adsorb molecules having a dimension less thanabout 12 A. and will exclude a material Whose minimum moleculardimension is above l2 A.

The synthetic crystalline partially dehydrated metallo alumino silicateZeolitic adsorbents are presently available items of commerce marketedby Linde Air Products Company, 30 E42nd Street, New York 17, New York,under the name lof Molecular Sieves 4A, 5A, 13X, etc.

The present metallo alumino silicates adsorb polar molecules to acertainement. In gasoline treating this interferes with thefractionation of gasoline hydrocarbons as a function of molecular shape.Accordingly it is contemplated in this invention to contact the feedstream first with a material which exhibits very strong adsorptiveforces for these polar materials and remove them from the stream to betreated. This pre-adsorption or pre-treating of the feed may beaccomplished by contacting the feed stream with an inorganic halide suchas copper chloride, calcium chloride, magnesium chloride, and the like.In this way large and highly polar materials such as ethers, thioethers,water, alcohols, mercaptans, and amines are readily removed from thefeed. Also removable in thisy way are the highly polar nitrogen andsulfur compounds which commonly occur in small amounts in gasolines.These specifically include such materials as thiophene and the alkylatedthiophenes, pyridine and alkylated pyridines. Thus this pre-treatmentremoves these polar materials and prevents them from interfering withthe subsequent fractionation in which the feed is separated into streamscontaining components of a specific molecular size or structure. Y

Although the pre-adsorption step prevents rapid deactivation of the mainadsorbent beds, some deactivation may' eventually occur. It is withinthe contemplation of this invention to regenerate the adsorbent by hightemperature stripping with steam etc. to desorb impurities, with hot uegas, to burn off the impurities as in catalyst regeneration, or both.

The process of this invention and the modifications thereof, as well asseveral forms of apparatus employed to carry out the process, will bemore readily understood by reference to the accompanying drawings, eachof which is described in connection with its application to thefractionation of gasoline as a specific example and in which:

Figure 1 shows a schematic flow diagram of a simple modification of theprocess of this invention adapted to contact continuously a feedgasoline stream with two fixed beds of adsorbent and utilizes either aliquid or vapor phase feed contact with a relatively low boilingdisplacement exchange recycle stream,

Figure 2 shows a modification of the process of Figure l adapted to theuse of a recirculatng or moving adsorbent stream, 1

Figure 3 shows a third modification of the present process in which therecirculated displacement exchange stream is of any intermediate boilingrange or boiling .point With respect to the unadsorbed stream and whichis therefore heart cut from the unadsorbed or rainate portion of thefeed,

Figure -4 shows another modification of this invention in which thedisplacement exchange stream is of an intermediate boiling point orboiling range with respect to both the adsorbed and unadsorbed streamsand is thus heart cut from both of these streams for recycle,

Figure 5 shows still another modification of this invention which isapplied to the successive contact ofthe feedstock in two or moreadsorbent stages, for example to adsorb normal olefins from the feed inthe first stage to recover them for blending into a high knock ratinggaso.

line and adsorbs normal paraffins in the second stage to reject them asa low antiknock rating product stream, and Figure 6 shows an alternatecontrol valve connection which causes the feed and theexchange-displacement streams to ow in opposite directions through theadsorbent beds.

Example I Referring now more particularly to Figure l, the simplestmodification of the present invention is shown in the form of aschematic flow diagram. Two adsorbers 10 and 12 packed with a compactmass of granular metallo alumino silicates having pore openingsapproximating 5 A. are shown. Adsorbers 10 and 12 are used inalternation with each other and the appropriate flow changes areeffected by means of four-way control valves 14 and 16 actuated by cycletimer 18. In the position shown adsorber 10 is being desorbed whileadsorber 12 is contacting fresh feed. Vessel 20 is provided as apre-adsorber or guard chamber to remove highly polar materials from thefeedstock.

A depentanized gasoline is passed in the vapor phase through line 22 ata rate controlled by valve 24 through pre-adsorber 20 wherein polarmaterials are removed from the feed. This pre-treated feed continuesthrough line 26 through the interconnected ports in valve 14 and thenthrough line 28 through adsorber 12. Herein an active displacementexchange` takes place between the normal parafiins in the gasolinestream and normal butane which is employed in this modification for therecycle stream and which saturates the adsorbent prior to contact withthe feed.l The normal butane recycle stream in this invention issubstantially lower in boiling point than any component of the feed. Thenormal butane pre-saturating the adsorbent is exchanged with the normalparafiins of the feed stream so that the adsorbent in adsorber 12finally becomes substantially saturated with these heavier normalparafiins. The effluent or raffinate stream from adsorber 12, containingthe non-adsorbable gasoline components together with the exchangednormal butane, passes on through line 30 through the interconnectedports in valve 16 and through line 32 into raffinate fractionator 34.This distillation column is provided with an overhead condenser 36 andreboiler 38. The raffinate is distilled separating the normal butanefrom the normal paraffin-free gasoline. The normal butane recovered fromthe gasoline is passedin the vapor phase through line 40 at a ratecontrolled by valve 42 into displacement exchange recycle line 44. Thetreated gasoline is removed from the bottom of the column and is passedto further processing or storage facilities not shown through line 46 ata rate controlled by valve 48, Because of the elimination of normalparafiins from this gasoline stream, the antiknock rating is readilyincreased by 7 to l0 points.

The normal butane exchange displacement recycle stream ows on throughline 44, through the interconnected ports of four-way control valve 14,and then through line 50l to adsorber 10 which is now in the desorptionpart of the cycle. The normal butane passes in the vapor phase throughthe adsorbent saturated with normal parains from the previous feedcontacting step. A reverse displacement exchange takes place whereby thenormal parains from the gasoline are displaced from the adsorbent and itadsorbs normal butane instead. Flowing from the top of adsorber 10through line 52 is a desorbed extract stream comprising a rich mixtureof normal paratiins desorbed from the adsorbent and normal butane usedin their desorption. This stream passes through the interconnected portsof valve 16 on through line 54 into extract distillation column 56,provided with overhead condenser 58 and reboiler 60. The normal butanepresent in the extract stream is distilled from the normal paraflinsremoved from the gasoline feed. The

normal butane ows through line 60 in the vapor phase at a ratecontrolled by valve 62 and is returned to and through displacementexchange recycle manifold 44. The very low antiknock extract, comprisinga concentrated mixture of normal paraflins, is removed from the systemthrough line 64 at a rate controlled by valve 66. Thus the highantiknock fraction is produced from the process through line 46containing substantially no normal para'ins, while the low antiknockgasoline fraction is produced through line 64 containing substantiallyall of the normal parans of the feed.

In the event that the feed stream contains normal butane, the netproduct of normal butane from the system over and above that requiredfrom the displacement exchange recycle may be removed through column 34via line 68 at a rate controlled by valve 70, or it may be re movedthrough column 56 through line 72 at a rate controlled by valve 7 4.

In the foregoing example it should be noted that the displacementexchange recycle stream consisted of normal butane vapor which islighter or has a lower boiling point than any of the components presentin the feed stream. It should also be noted that both the adsorption anddesorption steps of the process are conducted in the vapor phase.

Example Il In the present invention it has been found that olenhydrocarbons of the straight chain type are more strongly adsorbed thanare normal paraffins having the same number of carbon atoms as theolefin. It has been determined that the metallo alumino silicateadsorbents appear to have about an equal preference for a straight chainolefin and for a straight chain parain having three more carbon atomsper molecule than the olefin. This discovery is utilized according tothe present invention by modication of the process described inconnection with Figure 1 so as to employ low molecular weight olefin asthe exchange displacement recycle and which has about three carbon atomsper molecule less than the mol average of the more readily adsorbableparafins. In this case gaseous ethylene is used as the olefin and isfound to displace very effectively from they adsorbent the normalparaflins adsorbed from the gasoline. In Figure 1 the feed stream llowsas before through adsorber 12 into fractionator 34. In adsorber 12 thegasoline normal paraflins are adsorbed on the adsorbent displacingethylene therefrom, and in column 34 the gaseous ethylene is strippedfrom the Vnonadsorbed rainate gasoline and recireulated through line 44.The gaseous ethylene flows from line 44 through adsorber 10 into extractstill 56. The gaseous ethylene in adsorber 10 exchanges with thegasoline normal paraffins on the adsorbent and extract still 56 stripsthe gaseous ethylene for recirculation from these gasoline normalparaflins. It is found that the olenfin in this case is somewhat moreeffective in displacing gasoline normal parafns from the adsorbent thanwas the normal butene.

Example III The process shown in Figure l is also readily applicable tothe treatment of relatively narrow boiling range feed streams using as adisplacement exchange recycle stream a component which has anintermediate separation factor between the two fractions which it isdesired to separate from the feed. For example, in the process shown inFigure l a C6 cut of cracked (olenic) gasoline is passed in the vaporphase through adsorber 12 in contact with the adsorbent which is alreadysaturated with normal octane as the displacement exchange component. Thenormal octane is of an intermediate adsorbability between the normalhexene for which the adsorbent exerts strong adsorptive forces, andnormal hexane for which the adsorbent exhibits weaker adsorptive forces.The rainate from adsorber 12 consists of the normal octane recyclecomponents and the nonadsorbed raiinate cempauents, :in this .casecomprising normal hexane. In raffinate still 34 the normal hexane isproduced from the top of the still through line 68 at a rate controlledby valve 70 while the recycle component normal octane accumulates at thebottom of column 34 and is recirculated in the vapor phase through line76 controlled by valve 78 wherefrom it passes through line 80 intorecycle manifold 44. The normal octane flows through adsorber 10 whichis in the desorption part of the cycle and here it exchanges with thenormal hexene to produce an extract stream through line 52 comprisingnormal octane and normal hexene. This extract ows t0 fractionator 56 inwhich the normal hexene is produced as an overhead product through line72. It has a. relatively high knock rating and may, if desired, becombined with other high antiknock rating components to produce aquality gasoline. The normal octane recycle component is removed fromthe bottom of still 56 through line 79 and is controlled by valve 82 andpasses through line 84 back into recycle manifold 44 for recirculationin the system.

In this modification it is noted that the displacement exchangecomponent is of intermediate adsorbability between normal hexene andnormal hexane but it is of a higher boiling point so that it is producedfor recycle as a bottoms product in both the extract and ratiinatestills.

Example IV The process shown in Figure l was also applied to the vaporphase removal of normal paraflins from a depentanized light gasolinewhich had been reformed over a platinum catalyst. Normal pentane wasemployed as the displacement exchange recycle stream. The feed had aknock rating (motor method, clear) of 66.8. Using a bed of metalloalumino silicate adsorbent having 5 A. pores the raffinate or unadsorbedtreated gasoline had a knock rating of 78.4 while the adsorbed normalparaffin or extract stream had a knock rating 17.2. The leaded knockrating of the treated gasoline raffinate (research method-H ml. TEL) was97.9. The normal parain recycle adequately displaced and exchanged withthe gasoline normal parains from the adsorbent so that continuedtreatment of the feed gasoline was permitted.

Example V The treating of reformed depentanized gasoline, discussedimmediately above, was continued through 30 cycles, contacting the feedgasoline to adsorb normal paraflins in alternation with a displacementexchange step with normal pentane vapors to regenerate. Over this periodno decrease in the quantity adsorbed or the ability of the adsorbent toremove normal paraflins from the feedstock was noted. In one run an F-2clear octane rating of the adsorbed material of as low as 9.8 was notedand simultaneously the raffinate knock rating (F-l clear) was 83.7. Theleaded knock ratings of the unadsorbed phase in each of the 30 cyclesall fell between 97.5 and 98.3. Example VI The process shown in Figure lwas applied to the treating of light alkylate having a clear researchoctane rating of 96.4. This material contains highly branchedhydrocarbons and substantially no straight chain hydrocarbons. Thevolume of the feed which was adsorbed on the adsorbent was substantiallyzero at 280 F. and the unadsorbed raffinate product had the same knockrating of 96.4. n

Example VII The process of Figure l was applied to the removal of normalparains from a catalytically hydrocracked gasoline boiling between F.and 402 F. The feed had a research octane rating with 3 ml. TEL of 94.9.At an adsorption temperature of 403 F., approximately 6 volume percentof the feed was adsorbed and the unadsorbed rali'inate gasoline had aresearch octane rating witl13 ml. TEL of 97.3..

` adsorbed gasoline raffinate had a research octane rating-l-3 ml. TELof 88.3 average. The knock rating of the feedstock was 76.0.

Example IX In a pair of identical 30 cycle 4tests on platinumreformedlight gasoline, the process of Figure 1 was first employed using normalpentane as the exchange displacement recycle stream. In the first case adepentanized platinum reformed gasoline having a research octane ratingof 3 ml. TEL of 89.8 was treated to produce an unadsorbed gasolinerainate having an average knock rating of 96.2. This is an averageincrease of 6.4 octane numbers.

In the second case, ya dehexanized platinum reformed light gasoline,having a research octane rating of 91.0 (with 3 ml. TEL), was treatedunder identical conditions to produce an unadsorbed gasoline raffinateproduct having an average knock rating of 97.9 for an average increaseof 6.9 octane numbers.

Example X In the process of this invention employing the metallo aluminosilicates as adsorbents, it is found that in the liquid phase theadsorbent has a tendency to adsorb the lower molecular weight normalparains in preference to the higher molecular weight normal parains.-This is just the reverse of the tendency for adsorption in the vaporphase. Applying this inthe process of Figure 1, a C5 to C10 gasoline wastreated using normal butane in the liquid phase as the desorptionexchange recycle. In this case the feed passes through line 22 into andthrough adsorber 12 wherein the normal paraflns in the C5 to C range areadsorbed and exchanged for normal butane in the vapor phase. Thenonadsorbed high knock rating gasoline is fractionated in raflinatestill 34 .producing a bottoms product of high antiknock rating gasolineand the normal butane is produced as an overhead product. In thismodification the normal butane is produced in the liquid phase throughline 86 controlled by valve 88 and passed into and through recyclemanifold `44 Ato adsorber 10 which is in the desorption part of thecycle. Adsorber 10 is contacted with liquid normal butane and itdisplaces and exchanges with the adsorbed C6 to C10 normal parafiinsadsorbed from the gasoline during the previous cycle. The extract streamows through lines 52 and 54 into extract still 56. Here the displacedlow antiknock rating normal parains are produced from the bottom of thecolumn, the recycled normal butane in the liquid phase is removed fromthe top of the column through line 90 controlled by valve 92, and isreturned through manifold 44 to contact further quantities of richadsorbent.

In the foregoing example, because of the change in phase betweenadsorption and desorption and because of the reversal of the preferenceof adsorption, both the adsorption and desorption steps aresubstantially 100% efiicient.

Referring now more particularly to Figure2 a modification of the processshown in Figure 1 is described in which a recirculating stream ofadsorbent is employed. The inlet and outlet cycle valves have beeneliminated. In this fgure'the essential elements of the presentinvention include adsorption zone 100, desorption zone 102', solidsconveyor 104, raffinate still 106, and extract still 108. Feed gasolineis passed through line 110 at Aa rate controlled by valve 112 throughadsorption zone 100 in which the normal paraflins and other straightchain hydrocarbons are adsorbed thereby displacing and'cxchanging withthe recycle components saturating the adsorbent. The raffinate passesthrough line. 114 to rafnate still 106. Reboiler 116 and overheadcondenser 118 are provided. The unadsorbed raffinate gasoline having ahigh `antiknock rating is produced through line 120 controlled by valve1 22 as a product of the process'. The exchange displacement recyclestream separated from the raffinate passes in the vapor phase throughline 124 into recycle manifold 126 and is introduced into desorptionzone 102. Herein the recycle stream exchanges with and displaces theadsorbed normal parafins from the feed producing an extract which flowsthrough line 128 into extract still 108. Reboiler 130 and overheadcondenser 132 are provided. Herein the extract is separated into a lowantiknock rating gasoline, consisting essentially of normal paraflins,which is produced as a product through line 134 controlled by valve 136.The displacement exchange components separated from the extract passthrough line 138 controlled by valve 140 into recycle manifold 126. Anycomponents occurring in the feed which are the same as those used forthe exchange displacement cycle can be accumulated as an excess in thesystem and can be produced therefrom as products from eitheror both ofraffinate still 106 or extract still 108 through lines 142 and 144respectively.

In this modification the adsorbent passes downwardly by gravity as asubstantially compact moving bed through adsorber 100 exchanging itsadsorbed recycle components for the adsorbable straight chain componentsof the feed. The rich adsorbent is then conveyed through conveyor 104and introduced into desorption zone 102. Here it passes downwardly as amoving bed in contact with the displacement exchange recycle stream. Incontact therewith it gives up its adsorbed straight chain gasolinehydrocarbons and adsorbs components of the recycle stream thusproducinga regenerated adsorbent and the extract. The regeneratedadsorbent is introduced through line 146 into the top of adsorption zone100 for repassage therethrough.

In the process of Figure 2 utilizing a movingbed of granular contactmaterial, it is within the contemplation of this invention to employ anyor all of the Well known steps and apparatus elements characteristicallyemployed with moving bed processes. Since these are well known they havenot been detailed but are well understood by those skilled in the art.It is also contemplated to use the Same feed pre-treating stepsdescribed in connection with Figure 1 in the processes described inconjunction with Figures 2 through 6. y

Referring now more particularly to Figure 3, a schematic flow diagram ofthis invention is shown modified so as to employ a component of the feedstream as the recirculated exchange displacement component for desorbingthe adsorbed materials from the feed.

Example XI In Figure 3 the essential elements of the process includeadsorbers 150 and 152, control valves 154 and 156,- cycle timer operator158, extract still 160, and rafiinate heart cutting stills 162 and 164.The adsorbent used is the metallo alumino silicate having pores ofapproximately 5 A. size. A light fraction of gasoline, reformed on aplatinum catalyst, contains in addition to the aromatic hydrocarbonshaving high antiknock ratings, the iso and normal hexanes, heptanes,octanes, and nonanes with relatively low antiknock ratings. The feedintroduced through line 166 controlled by valve 168 through theinterconnected ports of valve 154 through first adsorber 152 in whichthe adsorbent is saturated with normal hexane. 'Ihe raflnate consistingof aromatic hydrocarbons in this boiling range and the branched chainisomers of hexane, heptane, octane, and nonane together with thedisplaced and normal hexane flows through line 1'69 `through theinterconnected ports of control valve 156 through line to the firstheart cutting column 1,62. The raffinate heart cutting stills areprovided with over- 11 head condensers and bottoms reboilers as inprevious examples. The overhead product from still 162 is producedthrough line 172 controlled by valve 174 and consists of iso-hexane andany lower boiling components. The bottoms product from the iirst stillcontains the displaced normal hexane together with the unadsorbedbranched chain hydrocarbons in the C through C9 range and unadsorbedaromatic hydrocarbons in this same boiling range. rThis material owsthrough line 176 controlled by Valve 178 into second heart cutting still164. The lightest material in this stream is the displacement exchangerecycle stream of normal hexane. The net product of normal hexane isremoved from the top of the column through line 180 controlled by valve182 and the remainder is removed as an overhead vapor product throughline 184 controlled by valve 186 as part of the exchange displacementrecycle stream. The bottoms product is removed from still 164 throughline 188 at a rate controlled by valve 190 and consists of theunadsorbed aromatic hydrocarbons and branched chain hydrocarbons boilingin the C6 to C9 range. This material together with the iso-hexaneproduced through line 172 may be combined if desired to produce highantiknock rating fuel substantially freed of normal parains.

still is also provided with an overhead condenser and bottoms reboiler.Herein the normal hexane, Sutlicient to make up the required amount ofdisplacement exchange recycle, is removed in the vapor phase throughline 196 controlled by valve 198 and combined with the overhead vaporfrom second heart cutting still 164 in recycle manifold 192. A netproduct of normal hexane may be produced, if desired, through line 200controlled by valve 202 from the top of still 160. The adsorbed normalparains in the C8 through C9 range are removed from the bottom ofextract still '160 through line 204 at a rate controlled by valve -6 andsent to further processing or storage facilities not shown. Thisconcentrate consists of a very low antiknock rating gasoline stream.

Referring now particularly to VFigure 4, the schematic ow diagram ofanother modication of the process of this invention is shown in whichthe exchange displacement recycle stream is a straight chain componentwhich has a boiling range intermediate both the unadsorbed raffinatecomponents and the adsorbed extract components of a wide rangefeedstock. The essential elements of the modification of Figure 4include adsorbers 210 and 212 containing metallo alumino silicateadsorbents having 5 A. pores, four-way control valves 214 and 216operated by cycle timer 218, the extract heart cutting stills 220 and222, and the raflinate heart cutting stills 224 and 226.

Example XII In the process of Figure 4 a gasoline fraction containingnormal and branched chain hydrocarbons of from 6 to l0 carbon atoms permolecule, and which may contain also naphthene and aromatic hydrocarbonsofrthis boiling range, is introduced through line 228 controlled byvalve 230, through control valve 214 and into adsorber 2'12 wherein thestraight chain normal. parains are adsorbed and exchanged with normaloctane which is the exchange displacement recycle component in thismodiiication. The unadsorbed hydrocarbons including the branched chainparaffins and other non-adsorbed hydroarbons together with the displacednormal octane flows through line 232 through valve 216 through line 234into rst column 224 of the raflinate heart cutting stills. Each of theheart cutting stills is provided with an overhead condenser and abottoms reboiler as in previous modifications.v The overhead productfrom first raiiinate heart cutting still 224 is removed through line 236controlled by valve 238 and consists of the unadsorbed branched chainhydrocarbons in the C6 through C8 range together with traces of thebranched chain C9 hydrocarbons. This is a high antiknock rating stream.The bottoms fraction from rst raffinate heart cutting still 224 isintroduced through line 240 controlled by valve 242 into secondraiiinate vheart cutting still 226. This stream consists of thedisplaced normal octane together with the remaining unadsorbed branchedchain hydrocarbons of the C9 and C10 species. In the second still 226the overhead vapor is recirculated through line 244 controlled by valve246 and consists essentially of the exchange displacement stream ofnormal octane together with a trace of iso-nonanes. The bottoms productfrom second still 226 is a high antiknock gas stream consisting ofbranched chain hydrocarbons of 9 and 10 carbon atoms per molecule. Thisstream may be produced separately or it may be passed through line 248controlled by valve 258 with the lower boiling branched chainhydrocarbons flowing through line 236. This stream is the rafnate andcontains the high antiknock components of the feed.

The normal octane exchange displacement recycle is returned through line252 through valve 214 into and through adsorber 210 which is in thedesorption part of the cycle. Herein it exchanges with and displaces theadsorbed straight chain paraflins previously adsorbed from the feed andproducing extract consisting of the desorbed C6 through C10 normalparaiiins and part of the recirculated normal octane. This extract flowsthrough line 254 and valve 216 through iirst extract heart .cuttingstill 220. The overhead product from the still consists of normal hexaneand normal heptane and is removed through line 256 controlled by valve258. The bottoms product consisting of normal octane, nonane, and decanepasses through line 260 controlled by valve 262 into second extractheart cutting still 222. Hereinthe recirculated normal octanedisplacement exchange stream is removed as an overhead product throughline 264 controlled by valve 266 and combined with the overhead productfrom the second eiuent heart cutting still 226 for recirculation to theadsorbent being desorbed. The bottoms fraction of still 222, owingthrough line 268 controlled by valve 270 contains the normal straightchain paraiins having 9 and l0 carbon atoms per molecule and which maybe combined with the lighter normal parafns produced overhead from still220 to produce a low antiknock rating gasoline through line 272. ltshould be noted in the present case that the normal octane recycleemployed iny this modication is in the liquid phase while the feed tothe adsorbers is passed in the vapor phase. Because of the intermediateadsorption preference for the normal octane, it is recovered from theextract and from the raffinate by a double heart cutting distillation.

Referring now Vto Figure 5, a still further modification of the processof this invention is shown which is especially adapted to the treatmentof cracked gasoline streams containing both normal and branched chainparafn and olefin hydrocarbons. The esential elements of this modicationinclude olefin adsorbers 280 and 282, with associated four-way controlvalves 284 and 286, paraffin adsorbers 288 and 290 with associatedcontrol valves 292 and 294, olefin extract still 296, paraffin extractstills 298 and 300, and rafiinate still 302. All of these stills areprovided as before with overhead condensers and bottoms reboilers. Theadsorbers contain metallo alumino silicate adsorbent havingapproximately 5 A. pores. It is found that because of the polar natureof normal oleiin hydrocarbons theyfare considerably more stronglyadsorbed than normal parafiins having the same number of carbon atoms.Therefore in this modificationthe feed stream is contacted twice insuccession lwith the adsorbent, first to adsorb normal olefins from thefeed and second to adsorb normal paraffins from lthe first adsorberraffinate to produce a product raffinate of a high antiknock rating.This modification also permits the separate recovery and reuse of thenormal olefins which have relative high antiknock rating and rejectionof normal paraffins which do not. Example X III A`cracked gasolinefeedstock and containing normal and branched chain paraffins and'olefinshaving from 6 to 9 carbon atoms per molecule boiling below about 425 F.is passed in the vapor phase through line 304 controlled by valve 306through control valve 284 to olefin adsorber 282 previously ksaturatedwith a first displacement exchange recycle stream consisting of normalparafiins in the C10 and C11 range, i.e. those which boil in or abovethe upper gasoline boiling range. The normal olefins are adsorbed hereinand produce a first raffinate consisting of the unadsorbed branchedchain parafiins as well as the unadsorbed branched chain and normalolefins together with the displaced higher normal paraffins of the firstdisplacement exchange recycle stream. vThis first raffinate fiowsthrough line 306 and control valves 286 and 292 into paraffin adsorber290. Here the higher normal paraffins of the first displacementexchange' recycle stream together with the normal paraffins of thefeedstock are adsorbed and displace a relatively low molecular weightolefin hydrocarbon, in this case normal pentene, or other olefin boilingnear the lower end of the gasoline boiling range, e.g. onvthe order of50-100 F. The second raffinate produced from adsorber 290 consists ofthe unadsorbed branched chain paraffins and olefins of the feedstocktogether with the normal pentene which is the second exchangeydisplacement component. This material flows through line 308 and valve294 and through line 310 into rafiinate still 302. The overhead productfrom raffinate still 302 consists of substantially pure normal pentene,which is the second exchange displacement recycle stream. This materialis recirculated through line 312 controlled by valve 314 and isrecirculated together with the normal pentene overhead vapor fromparaffin extract still 298, hereinafter described. The bottoms productfrom raffinate still 302 is produced through line 316 controlled byvvalve 318 and consists of the unadsorbed iso-olefins and iso-paraffinsof the feedstock having between 6 and 9 carbon atoms per molecule. Thisis aY high antiknock rating gasoline stream.

The first recycle stream employed to exchange with and displace theVadsorbed normal olefins is a relatively heavy normal parafiin mixtureof C10 and C11 hydrocarbons. This material is recirculated through line320 through valve 284 and through olefin adsorber 280 which is in thedesorption part of the cycle. Here the first recycle stream paraffinsare adsorbed and displace the adsorbed normal olefins from theadsorbent. The olefin extract consisting of normal olefins in the C6through C9 range together with the first recycle C10 and C11 normalparaffins flows from adsorber 280 through line 322, valve 286, line 324into olefin extract still 396. The adsorbednormal olefins are producedtherefrom as an overhead prod uct through line 326 controlled by valve328 and may be blended with the high antiknock rating unadsorbedcomponents of the feed flowing through line 316 from the bottom ofraffinate still 302. The normal olefin-free first recycle stream isremoved from the bottom of olefin extract still 296 through line 330controlled by valve 332 and is recirculated through line 320 to displaceadditional normal olefins from the adsorbent.

14 stream passes through line 334, valve 292, into and through paraffinadsorber 288 which is being desorbed1 The parafiin extract is producedtherefrom through line t 336'and'consists of normal pentene of thesecond recycle stream together with desorbed normal paraffins in the C6through C9 range. This parafiin extract flows through valve 294 and line338 into paraffin extract still 298. The second recycle stream being oflower boiling point is produced as an overhead vproduct through line 340com trolled by valve 342. This normal pentene is combined with thatseparated from the rafiinate in rafiinate still 302 and the combinedstream is recirculated as the second re cycle stream in the process.

The desorbed normal paraffins in the C6 through C@ range together withtraces of the C10 and Cn heavy par afiin of the first recycle stream areproduced as a bottoms product from parafn extract still 298 through line344 controlled by valve 346 and are introduced to second paraffinextract still 300.' The overhead product from this still consists of thedesorbed normal parafiins originating in the feed stream, namely the C6through C9 paraliin hydrocarbons, and they are produced as a lowantiknock rating gasoline product through line 348 controlled by valve350. Because the parain extract was derived in adsorber 288 from anadsorbent previously contacted with the olefin raliinate from adsorber280, which in turn had been previously desorbed by the first recyclestream consisting of heavy parafiins, the desorbed normal paraffins ofthe feed are contaminated with small amounts of the C10 and C11 normalparaliins of the first recycle stream. These materials are separated asa bottoms product from still 300, are recirculated through line 352controlled by valve 354 and pass through line 356 into admixture withthe heavy paraffins of the first recycle stream produced as a bottomsproduct from olefin extract still 296. This heavy paraffin mixtureprovides the first recycle stream employed to exchange with and displacethe adsorbed normal olefins.

In the modification of the process one or more normal paraffins having aboilingpoint above the end point of the feedstock is employed as thefirst recycle stream to exchange with and displace the normal olefinsfirst adsorbed from the feedstock and from which such heavy paraffinsare readily separable by distillation. The second recycle stream in themodification comprises a normal olefin having a normal boiling pointbelow that of the lightest component of thelfeed stream and which, because of its greater adsorbability,.can successfully be desorbed anddisplace higher molecular weight normal parafiins. It is also readilyseparable by distillation from the desorbed normal paraliins ofthefeedstock.

In Figure 6, the schematic flow .diagram of Figure l has been modifiedso that valves 14' and 16 route the feed up through the adsorbent bedsin adsorbers 10 and 12' and the exchange-,displacement recycle downthrough it. The reverse type of opposed flow canof course be used ifdesired by appropriate reconnection of the valves. Such opposed ow offeed and recycle streams can be used in ,any of the processes describedand illustrated above, and has beenrfound to be a highly eflicientcontacting method. y Y

The foregoing description of several modifications of the presentinvention will serve to explain to those skilled in the art theprinciples of the present invention and the application thereof tovarious complex mixtures. Although the examples herein given have beendirected to the fractionation of complex mitxures of hydrocarbons, thisis not to be understood as a limitation of the process of this inventionsince the same principles may readily be applied to other mixtures ofmaterials. Furthermore, the adsorbent materials specified in theforegoing examples have been specified as the metallo alumino silicatepresently available. This also is not intended to be a limitation sinceother adsorbents can be substituted de pendingonthe nature of the feedstream and the`adsorp.

tion characteristics on the materials to be adsorbed therefrom.V Theseparticular inorganic adsorbents with vtheir uniform poresizes have beenspecified here since they are preferred in the illustrative applicationsof the process of this invention to the removal of straight chainparaflins and olelins from gasoline streams. These hydrocarbons areusually present in a minor proportion, particularly with reformedgasolines, so that the unadsorbed materials consist of aromatic andbranched chain paraffin hydrocarbons of high antiknock rating.

The process of this invention thus consists of an improved fractionationprocess for complex mixtures employing the principles of solidadsorption and distillation in such a way so as to remove specificmaterials from the feed stream by means of the adsorbent and whereby theordinary heating and gas stripping or liquid washing of the richadsorbent have been completely eliminated. The process of this inventionmay be operated under pressure or under vacuum, and the actual operatingpressures are actually determined by the pressure at which the feedstream is available and its boiling range, and whether the materialbeing contacted is desirably in the vapor phase or the liquid phase. Theproper operating pressure can be determined by those skilled in the artfrom known physical characteristics of the materials to be separated;namely the bubble point and dew point of complex hydrocarbon mixturesand the known way in which these change with pressure. The adsorptiontemperatures employed in the process of this Ainvention are alsodetermined by the physical characteristics of the feed stream and theoperating pressure and also whether a vapor phase or a liquid phaseContact is desired. In the complex gasoline streams the operatingtemperature is largely determined by the dew point and the bubble pointof the stream at a given operating pressure. For example, adsorptiontemperatures above the dew point will obviously be in the `vapor phasewhile operating temperatures below the bubble point will be in theliquid phase. It is within the contemplation of the present invention toadsorb to feed stream at a temperature between its bubble point and itsdew point so that a mixed phase adsorption or displacement exchangedesorption will be maintained for some special streams and obviously thefeed contact may be in the vapor phase followed by recycle streamContactin the liquid phase, or vise versa, if desired.

A particular embodiment of the present invention has been hereinabovedescribed in considerable detail by way of illustration. It should beunderstood that various other modifications and adaptations thereof maybe made by those skilled in this particular art without departing fromthe spirit and scope of this invention as set forth in the appendedclaims.

We claim:

1. The process for treating a petroleum hydrocarbon feed mixture boilingover a relatively wide range within the gasoline boiling range andcomprising straight chain and non-straight chain hydrocarbons, whichprocess comprises: (1) contacting said mixture with a lean solidgranular adsorbent essentially comprising a partially dehydratedzeolitic metallo alumino silicate having substantially uniform pores ofabout A. in diameter and having adsorbed lthereon a displacementexchange fluid of relatively narrow boiling range consistingsubstantially only of'straight chain hydrocarbon components of said feedmixture, whereby there is obtained a rainate product comprisingnon-adsorbed non-straight chain hydrocarbon components of the feedmixture in admixture with desorbed displacement exchange fiuid, and arich adsorbent comprising saidgranularV silicate having adsorbed thereonstraight chain components of the feed mixture; (2) separating saidraffinate product from said rich adsorbent; (3) contacting said richadsorbent with said displacement exchange fluid whereby the adsorbent isreturned to its lean state and there is obtained an extract 16 productcomprising desorbed straight chain hydrocarbon components of the feedmixture in admixture with said displacement exchange tiuid; (4)separating said extract product from the lean adsorbent; (5) returningthe said lean adsorbent obtained in step (4) to step (1); (6) treatingthe raffinate product obtained in step (2) to separate said non-adsorbednon-straight chain hydrocarbon components of the feed mixture from saiddisplacement exchange fiuid; (7) treating the extract product obtainedin step (4) to separate therefrom a fraction of relatively narrowboiling range; and (8) returning at least a part of said fraction ofrelatively narrow boiling range to step (3) as said displacementexchange fluid.

2. A process as defined by claim l wherein, in step (l), said feedmixture is maintained in the vapor state and, in step (3), saiddisplacement exchange fluid is maintained in the vapor state.

3. A process as defined by claim l wherein at least part of thedisplacement exchange fluid which separated from the raffinate productin step (6) is returned to step (3).

4. A process as defined by claim 1 wherein the said displacementexchange fiuid is a relatively narrow boiling range heart-cut of thesaid extract product.

5. The process for treating a petroleum hydrocarbon feed mixturecomprising straight chain and non-straight chain hydrocarbons containingfrom 6 to about 9 carbon atoms, including isohexane and n-hexane, whichprocess comprises (1) contacting said mixture with a lean solid granularadsorbent comprising a partially dehydrated zeolitic metallo aluminosilicate having substantially uniform pores of about 5 A. in diameterhaving n-hexane adsorbed thereon, whereby there is obtained a raffinateproduct comprising non-adsorbed non-straight chain hydrocarboncomponents of the feed mixture, including isohexane, in admixture withdesorbed n-hexane, and a rich adsorbent comprising said granularsilicate having adsorbed thereon straight chain components of the feedmixture; (2) separating said raffinate product from said rich adsorbent;(3) contacting said rich adsorbent with n-hexane, whereby the adsorbentis returned to its lean state and there is obtained an extract productcomprising desorbed straight chain hydrocarbon components of the feedmixture, including n-hexane', (4) separating said extract product fromthe adsorbent; (5) returning the said lean adsorbent obtained in step(4) to step (1); (6) distilling the rainate product obtained in step (2)to obtain a raffinate overhead fraction consisting essentially ofisohexane and a raffinate bottom product comprising n-hexane andnon-straight chain hydrocarbon components of the feed; (7) distillingsaid raffinate bottoms product to separate n-hexane therefrom; (8)distilling the extract product obtained in step (4) to separate n-hexanetherefrom; and (9) returning separated n-hexane to step (3).

6. The process of treating a petroleum hydrocarbon feed mixturecomprising straight chain and non-straight chain hydrocarbons containingfrom 6 to about 9 carbon atoms, including n-octane, which processcomprises (l) contacting said mixture with a lean granular adsorbentcomprising a partially dehydrated zeolitic metallo alumino silicatehaving substantially uniform pores of about 5 A. in diameter havingn-octane adsorbed thereon, whereby there is obtained a raffinate productcomprising non-adsorbed non-straight chain hydrocarbon components of thefeed mixture in admixture with desorbed n-octane, and a rich adsorbentcomprising said granular silicate having adsorbed thereon straight-chainhydrocarbon components of the feed mixture; (2) separating saidraffinate product from said rich adsorbent; (3) contacting the said richadsorbent with n-octane, whereby the adsorbent is returned to its leanstate and there is obtained an extract product comprising desorbedstraightchain hydrocarbon components of the feed mixture, includingn-octane; (4) separating said extract product from the lean adsorbent;(5) returning the said lean 17 adsorbent to step 1); (6) distilling theraffinate product obtained in step (2) to separate n-octane therefrom;(7) distilling the extract product obtained in step (4) to separaten-octane therefrom; and (8) returning separated n-octane to step 3).

7. A process for treating a petroleum hydrocarbon feed mixture boilingover a relatively wide range within the gasoline boiling range andcomprising straight and non-straight chain paratlins and olefines, whichprocess comprises: (1) contacting said feed mixture with a lean firstsolid granular adsorbent comprising a partially dehydrated zeoliticmetallo alumino silicate having substantially uniform pores of about A.in diameter and having ladsorbed thereon a first displacement exchangeuid consisting essentially of straight-chain parain hydrocarboncomponents of said feed mixture boiling between relatively narrow limitsat the upper end of the boiling range thereof, whereby there is obtaineda first raffinate product comprising non-adsorbed non-straight chainhydrocarbon camponents of the feed mixture and non-adsorbed straightchain hydrocarbon components of the feed mixture in admixture with saidfirst displacement exchange fluid, and a rich first adsorbent comprisingsaid granular silicate having adsorbed thereon normal oleiinehydrocarbon components of the feed mixture; (2) separating said firstraffinate product from said rich adsorbent; (3) contacting said richfirst adsorbent with said first displacemnet exchange fluid, wherebythere is obtained said lean first adsorbent and a first extract productcomprising desorbed normal olefines in admixture with said firstdisplacement exchange fluid; (4) separating said first extract productfrom said lean first adsorbent; (5) treating the separated first extractproduct to separate said first displacement exchange uid therefrom; (6)contacting the separated first raffinate product with a lean secondadsorbent comprising Ia solid granular partially dehydrated zeoliticmetallo alumino silicate having substantially uniform pores of about 5A. in diameter and having adsorbed thereon a second displacementexchange fluid consisting essentially of normal olefine hydrocarboncomponents of the feed mixture boil- 18 ing between relatively narrowlimits at the lower end of the boiling range thereof, whereby there isobtained a second ranate product comprising non-absorbed nonstraightchain hydrocarbon components of the feed mixture in admixture with saidsecond displacement exchange fluid, and a second rich adsorbentcomprising said granular silicate having adsorbed thereon straight chainparaflin hydrocarbon components of the feed mixp ture; (7) separatingsaid second rafnate product from said second rich adsorbent; (8)contacting said second rich adsorbent with said second displacementexchange fluid, whereby there is obtained said second lean adsorbent anda second extract product comprising desorbed straight chain paranhydrocarbon components of the feed mixture in admixture with said seconddisplacement exchange tluid; (9) separating said second extract productfrom said second lean adsorbent; (10) treating the separated secondextract product to separate therefrom as separate entities said seconddisplacement exchange fluid and a fraction consisting essentially ofstraight-chain parain hydrocarbon components of the feed mixture boilingover relatively narrow limits at the upper end of the boiling rangethereof; and (l1) treating the separated second raffinate product toseparate said second displacement exchange fluid therefrom.

References Cited in the le of this patent UNITED STATES PATENTS2,306,610 Barrer Dec. 29, 1942 2,459,442 Lipkin Jan. 18, 1949 2,522,426lBlack Sept. 20, 1950 2,564,717 Olsen Aug. 21, 1951 2,621,149 Scott etal Dec. 9, 1952 2,643,972 Weedman June 30, 1953 2,678,132 Beard May 11,1954 2,712,008 Kirchner et al .Tune 28, 1955 2,768,221 Findlay Oct. 23,1956 2,776,250 Capell et al. Jan. 1, 1957 2,818,137 Richmond et al Dec.31, 1957 2,818,455 Ballard et al. Dec. 31, 1957

1. THE PROCESS FOR TREATING A PETROLEUM HYDROCARBON FEED MIXTURE BOILINGOVER A RELATIVELY WIDE RANGE WITHIN THE GASOLINE BOILING RANGE ANDCOMPRISING STRAIGHT CHAIN AND NON-STRAIGHT CHAIN HYDROCARBONS, WHICHPROCESS COMPRISES: (1) CONTACTING SAID MIXTURE WITH A LEAN SOLIDGRANDULAR ADSORBENT ESSENTIALLY COMPRISING A PARTIALLY DEHYDRATEDZEOLITIC METALLO ALUMINO SILICATE HAVING SUBSTANTIALLY UNIFORM PORES OFABOUT 5 A. IN DIAMETER AND HAVING ADSORBED THEREON A DISPLACEMENTEXCHANGE FLUID OF RELATIVELY NARROW BOILING RANGE CONSISTINGSUBSTANTIALLY ONLY OF STRAIGHT CHAIN HYDROCARBON COMPONENTS OF SAID FEEDMIXTURE, WHEREBY THERE IS OBTAINED A RAFFINATE PRODUCT COMPRISINGNON-ABSORBED NON-STRAIGHT CHAIN HYDROCARBON COMPONENTS OF THE FEEDMIXTURE IN ADMIXTURE WITH DESORBED DISPLACEMENT EXCHANGE FLUID, AND ARICH ADSORBENT COMPRISING SAID GRANDULAR SILICATE HAVING ADSORBEDTHEREON STRAIGHT CHAIN COMPONENTS OF THE FEED MIXTURE, (2) SEPARATINGSAID RAFFINATE PRODUCT FROM SAID RICH ADSORBENT, (3) CONTACTING SAIDRICH ADSORBENT WITH SAID DISPLACEMENT EXCHANGE FLUID WHEREBY THEADSORBENT IS RETURNED TO ITS LEAN STATE AND THERE IS OBTAINED AN EXTRACTPRODUCT COMPRISING DESORBED STRAIGHT CHAIN HYDROCARBON COMPONENTS OF THEFEED MIXTURE IN ADMIXTURE WITH SAID DISPLACEMENT EXCHANGE FLUID, (4)SEPARATING SAID EXTRACT PRODUCT FROM THE LEAN ADSORBENT, (5) RETURNINGSAID EXTRACT LEAN ADSORBENT OBTAINED IN STEP (4) TO STEP (1), (6)TREATING THE RAFFINATE PRODUCT OBTAINED IN STEP (2) TO SEPARATE SAIDNON-ADSORBED NON-STRAIGHT CHAIN HYDROCARBON COMPONENTS OF THE FEEDMIXTURE FROM SAID DISPLACEMENT EXCHANGE FLUID, (7) TREATING THE EXTRACTPRODUCT OBTAINED IN STEP (4) TO SEPARATE THEREFROM A FRACTION OFRELATIVELY NARROW BOILING RANGE, AND (8) RETURNING AT LEAST A PART OFSAID FRACTION OF RELATIVELY NARROW BOILING RANGE TO STEP (3) AS SAIDDISPLACEMENT EXCHANGE FLUID.